1990 Astro Engine Surges with Both Fuel Injectors

OK, so I'm trying to help the guy across the street fix his 1990 Astro Van. The problem is that the engine repeatedly surges and then almost stalls after about 1 minute after turning the key. When you disconnect one of the fuel injectors things work fine (there's only 2 because I'm guessing it's throttle-body injection?). Unfortunately, with one of the injectors disconnected, it means your only running on 3 cylinders, which isn't good.

Anyways, we just replaced the fuel filter, and that didn't seem to help. It looks like there is plenty of fuel coming out of the injectors. Can you adjust the mix on a throttle-body fuel-injection engine? I'm not sure what else to do, any help would be really appreciated.

Take a can of carb cleaner and spray it around the base of the TBI unit. If the idle surges and smoothes out you've found your trouble. Sounds to me like the gasket between the TBI/intake manifold has failed.